In a conventional switch-mode synchronous buck voltage regulator, under light load or no load conditions, the conduction state of the low-side switch may be long enough for the inductor current (IL) to decay to zero and start to reverse. This reverse inductor current (IL) will generate additional voltage stress across the low-side switch during the transition to and from the dead times because of the voltage drop in the body diode of the high-side transistor switch and the voltage spikes caused by parasitic components. As a result, the higher the negative inductor current, the higher the voltage stress. Thus, it is desirable to prevent excessive voltage stress on the low-side switch by limiting the negative inductor current in a switch-mode synchronous buck voltage regulator.
Furthermore, the turning off of the low-side transistor switch will cause high frequency oscillation at the switch node due to parasitic elements. Usually this oscillation frequency is much higher than the switching frequency. As a result, the output may see high frequency ripples, resulting in electromagnetic interference (EMI) that adversely affects the performance of other components circuit. Passive RC snubbers have been used to suppress the ringing. Although this prior-art method is effective, the RC snubber has reduced power efficiency.